- Capturing the image
- Camera settings
- Care and maintenance
- Custom functions
- Digital camera features
- Digital image file
- Digital image size and preview
- EOS MOVIE
- Exposure settings
- Flash basics
- Speedlite compatibility
- Speedlite range
- Speedlite zoom
- Flash on camera
- Dark backgrounds with flash
- Fill in flash
- Flash exposure lock and compensation
- Wireless flash
- Macroflash photography
- Bounce flash
- Flash synchronisation
- Stroboscopic flash
- Studio-style flash lighting with Speedlites
- Integrated Speedlite Transmitter
- Remote Release
- Focus points
- Image download
- Image compression
- Image information
- Image verification
- Introduction to digital photography
- Focal length
- All about apertures
- Lens speed
- Focusing and depth of field
- Black or white lenses
- Coloured rings
- Lens mount
- EF-S and field of view
- L-series lenses
- Fluorite, aspherical and UD lenses
- Prime and zoom lenses
- Image stabilisation
- Tilt and shift lenses
- Extension tubes
- Macro lenses
- Close-up lenses
- DO elements
- Fisheye lenses
- SubWavelength structure Coating
- Media cards
- Panoramic images
- Remote photography
- Scanning & copying
- Storage and archiving
- The digital darkroom
- White balance
Image verification: Canon data verification system
It is very easy to modify a digital image. Anyone with a basic knowledge of Photoshop software can add or remove elements of a photograph. This is not a problem if you are taking pictures for your own pleasure, but it is a serious issue for news agencies, forensic photographers and insurance companies. Most newspapers, for example, don’t allow anything other than basic retouching (dust removal, for example) and photographers have been fired for breaking the rules. But how can you tell if an image has been changed? Canon has one solution – data verification.
One advantage of the Canon system is that it costs the photographer nothing. There are no accessories to buy and no software to install. Everything you need is already available in the camera – providing you have one of the compatible models. All you have to do is switch on the data verification system. It is the end user of the image – the news agency or police department – which needs to buy the Canon Data Verification Kit to check the integrity of your image.
When you take a digital photo with certain EOS cameras, a code can be generated and attached to the image file. This code is based on the digital content of the image. At any time in the future, a Canon Data Verification Kit can be used to regenerate a code from the same image, or a copy of that image. If the first and second codes match, the image has not been modified. If the codes are different, it means that the content of the image has been changed.
The system is so precise that even a discrepancy of one bit between the two images will throw up an error. A bit is the smallest element of an image (there are 8 bits to a byte, and 1,048,576 bytes to a megabyte), so the system will pick up any change, however small. Here is how it works.
- Data from the image captured by the camera is compressed. This data is then arithmetically processed using a MAC (Message Authentication Code) secret key to create ‘Signature data A’. This is attached to the image data file as additional digital information.
- The verification system separates ‘Signature data A’ from the image file. The file is then processed again using the same MAC secret key that was assigned when the photo was taken. This produces a new file that is labelled ‘Signature data B’.
- If ‘Signature data A’ and ‘Signature data B’ match, then the image data has not been altered. Any difference between the two files shows that the second file is a modified version of the first. Since the same method can be used to verify whether image header information has been tampered with, the reliability of both the image and the attached information can be verified at the same time.
The great thing about data verification is that – as a photographer – it does not cost you a penny, providing you have a compatible camera. All you have to do is switch on the code generating system built into the camera and keep shooting. It is the newspaper picture desk or law enforcement agency that needs the data verification kits if they want to check the integrity of images.
The following cameras are compatible with the Canon Data Verification kits. The information in brackets shows the Personal Function or Custom Function number needed to activate the data verification system:
EOS-1Ds Mark II (P.Fn-31)
EOS-1Ds Mark III (C.Fn 1V-15)
EOS-1D Mark II (P.Fn-31)
EOS-1D Mark II N (P.Fn-31)
EOS-1D Mark III (C.Fn IV-15)
EOS 20D and 20Da (C.Fn-18)
EOS 30D (C.Fn-19)
EOS 5D (C.Fn-20)
Personal Functions (P.Fn) can only be set from a computer. Install File Viewer Utility (or EOS Viewer Utility) from the Digital EOS Solution Disk supplied with the camera. Connect the camera to the computer using the supplied interface cable and launch the viewer utility application. Click the Camera Settings button, then the Detailed Settings tab, then the Personal Functions button. In the new window, select the last of the Other Functions tabs at the right of the screen. Under P.Fn-31 tick the box for ‘Add original decision data’.
Custom Functions (C.Fn) can be set via the Menu screen on the back of the camera. Select Custom Functions from the Tool menu, then the appropriate custom function number (see above). Change ‘Add original decision data’ from ‘Off’ to ‘On’.
Using the digital EOS camera
When the image is taken, the image data is compressed using a MAC secret key to create a signature data file, which contains a verification code.
The signature data file and verification code is attached to the data file of the original image.
Using the verification kit
The Canon Data Verification kit creates a new signature data file from a supplied copy of the image file. If the new verification code matches the code embedded in the file, it means that the image is untouched. If there is a miss-match between the codes, the original image has been modified.
Canon is now on version three of its Data Verification Kit. Here is a brief guide to each of them.
Introduced with the EOS-1Ds in 2002. The Data Verification Kit DVK-E1 consists of a dedicated IC card and card reader, together with software for Windows 2000/XP. Discontinued.
Introduced with the EOS-1D Mark II; also compatible with the EOS-1Ds, EOS-1Ds Mark II, EOS-1D Mark II N, EOS-1D Mark III, 5D, 30D, 20D and 20Da. The kit consists of a dedicated SM (secure mobile) card reader/writer and verification software. The tiny SM card reader/writer is barely bigger than the cards it takes. It draws the power it requires from the USB port of the computer to which it is connected. The software is Windows 2000/XP compatible. Up to 100 images can be evaluated simultaneously. Discontinued.
Reuters is one of the world’s largest news agencies. They, like all other news agencies, have very strict rules about the use of Photoshop. Here is a summary:
“Materially altering a picture in Photoshop or any other image editing software will lead to dismissal. The rules are:
− No additions or deletions to the subject matter of the original image (thus changing the original content and journalistic integrity of an image)
− No excessive lightening, darkening or blurring of the image (thus misleading the viewer by disguising certain elements of an image)
− No excessive colour manipulation (thus dramatically changing the original lighting conditions of an image).”
For full details of the Reuters rules click here.